In medical field, safety of therapy or minimum invasive therapy which is light in patient's pain has become important. Along with that, techniques for designing or synthesizing safer materials or techniques for administration in vivo have been developed. One of them is technique of therapy or administration of drug through a tube of small inner diameter. By being the inner diameter of the tube small, it became unnecessary to incise patient's body, and a pain accompanied by inserting the tube into body was also greatly reduced. Therapy by catheter is a marked example of that. Another one is a technology relating to a biodegradable or bioabsorbable material which is not left in the body. A sewing thread or orthopaedic material made such as of polylactic acid, polyglycolic acid or polycaprolactone is used also in clinical site, and recently, many research results of regenerative medicine in which these materials were applied were reported. As to polymer particle which is degradable or absorbable in the body is also known mainly as a carrier of drugs (refer to Patent references 1 and 2).
Furthermore, at an incision accompanied by a surgical operation such as of liver, by injecting an embolization material into blood vessel beforehand, it is possible to firmly and quickly stanch to minimize bleeding. And, as a technique or therapy in which such embolization material is used, other applications than the prevention of bleeding, an application to an artery embolization in which nutrition for an unrecectable tumor is intercepted by hemostasis, and further, a chemical embolization therapy in which an anticancer drug and an embolization material are administrated together to maintain the anticancer drug concentration in the tumor high, are known. On the other hand, by development of catheter and its operation method, it has become possible to carry the microparticle carrier or embolization material to a specific site selectively and precisely.
As embolization materials, so far a gelatin sponge, polyvinyl alcohol, a degradable starch particle (DSM), an iodine addition products obtained from poppy seed oil, a cross-linked collagen fiber, an ethyl cellulose microcapsule, cyanoacrylate, stainless coil, etc., have been used. Among them, embolization material consisting of polymer particle can be, in a dispersed state in such as contrast agent, introduced into the body by injecting to an affected region by such as microsyringe via a microcatheter arranged in the body. Such embolization material of polymer particle can form an embolization by arriving at an affected region located in a deep portion.
However, there are following problems in the microparticle carrier consisting of polymer particle or the embolization material.
(1) Since its shape is irregular and particle size distribution is wide, there may be cases where its function cannot be exhibited at desired portion.
(2) In a tube of pharmaceutical and medical application devices such as catheter, needle or syringe, it may aggregate or its viscosity may increase to clog the tube. In particular, the clogging frequently occurs when a particle smaller than inner diameter of the catheter is passed through.
(3) It may not be able to be carried to a desired site since it aggregates or its viscosity increases in a normal blood vessel on the way to an affected region.
(4) In case where it is used as an embolization material, since its material quality is hard and does not fit to cross-sectional shape of a blood vessel, although it may decrease blood flow, it may not be able to perfectly embolize.
(5) Furthermore, as a degradable material in vivo, depending on a slight difference of environment where it is placed, such as whether it is a site contacting with blood or not, its degrading rate may change greatly.
(6) Since particle diameter is not appropriate, it may not be able to be indwelled at a desired site.
(7) In particular, in case of a particle which is smaller than inner diameter of the catheter, after passing through the catheter, since it is carried to an affected region in a crushed condition without recovering to its original shape, it may embolize at a farther site than desired.
As prior arts, particles consisting of polylactic acid (hereafter, referred to as PLA) or poly (lactic acid/glycolic acid) copolymer (hereafter, referred to as PLGA) which are biodegradable polymers (refer to Nonpatent reference 1), or a biodegradable material containing a specified agent are disclosed (refer to Patent reference 3), but since hydrophobicity of the these substrates are high, and there were problems of the above-mentioned (2) to (5).
On the other hand, an application to drug manufacturing or to veterinary drug of a technique in which a drug is mixed to a substrate polymer consisting of a structure such as PLA-PEG, PLA-PEG-PLA or PLGA-PEG-PLGA, as a block copolymer consisting of polyethylene glycol (hereafter, referred to as PEG) and PLA or PLGA, to sustain release the drug, is disclosed (refer to Patent reference 4). However, in this technique, it was impossible to control softness and necessary strength for molding of the substrate polymer, and there were problems in at least one of the above-mentioned (1) to (5).
Furthermore, an embolization material consisting of a water insoluble PEG-based copolymer is disclosed (Patent reference 5). However, in this case, too, it was impossible to control softness and necessary strength for molding of the substrate polymer, and there were problems in at least one of the above-mentioned (1) to (5) and (7).
As a technique for improving clogging in catheter tube when the above-mentioned biodegradable particle is carried by an injection from the catheter, a particle consisting of water insoluble polymer such as polyethylene glycol-based copolymer of which film tensile modulus is 1500 MPa or less, is disclosed (Patent reference 6). However, the technique disclosed here is, as indicated in the examples of the reference, nothing more than a technique of improving passing ability through catheter of a particle size smaller than inner diameter of the catheter tube, and since it is not an invention of improving passing ability of a particle of which diameter is larger than inner diameter of the catheter tube, a molecular weight range, composition or the like of the copolymer necessary for preventing clogging in the catheter tube of a particle having a diameter larger than inner diameter of the catheter tube, has not been found.
Furthermore, in Patent references 5 and 6, no reference is made about the problem (7) which relates to a recovery after passing catheter, i.e., molecular weight range, composition or the like of the copolymer necessary for the recovery, has not been found.    [Patent reference 1] JP-3242118C    [Patent reference 2] JP-3428972C    [Patent reference 3] JP-H5-969A    [Patent reference 4] JP-H5-17245B    [Patent reference 5] JP2004-167229A    [Patent reference 6] JP2004-313759A    [Nonpatent reference 1] Bastian P, Bartkowski R et al., Chemo-embolization of experimental liver metastases, European Journal of Pharmaceutics and Biopharmaceutics, 1998, vol. 43, p 243-254.